This invention relates to 1.times.N fiber optic couplers (N&gt;2) that are capable of coupling substantially equal amounts of power from an input optical fiber to three or more output optical fibers; it also relates to methods of making such couplers.
Methods of making 1.times.N couplers are disclosed in said related U.S. Pat. application Ser. No. 380,877. Protective coating is removed from a region of an input optical fiber intermediate the ends thereof, and protective coating is removed from an end of each of a plurality of output optical fibers. The coated portion of the input fiber is threaded through the aperture of a capillary tube until the uncoated region thereof is near the tube end. The uncoated regions of the output fibers are placed around that of the input fiber, and the uncoated regions of all of the fibers are simultaneously fed into the tube aperture until the uncoated regions extend through the midregion of the tube. In order to equally space the output fibers around the input fiber, the uncoated sections of the output fibers are glued to the input fiber prior to inserting the fiber bundle into the tube. The tube midregion is heated to collapse it about the fibers, and the central portion of the midregion is drawn to reduce the diameter thereof over a predetermined length.
Said related U.S. Pat application Ser. No. 223,423 teaches that tubes having bores of predetermined cross-section can be employed to facilitate the alignment of the output fibers around the centrally-disposed input fiber prior to the tube collapse step. The aperture is formed by a plurality of flattened walls, the dimensions and orientations of which are such that the cross-section of the aperture in the central region of the tube is symmetrical with respect to a plane passing through the longitudinal axis of the tube. At any cross-section of the aperture that is adjacent the coated regions of the fibers, each fiber coating contacts two walls of the aperture. The midregion of the tube is heated and collapsed about the fibers, and the central portion of the midregion is drawn to reduce the diameter thereof. For example, four fibers can be positioned in a triangularly shaped bore, three of the fibers being equally spaced about a central fiber. After the tube collapse step, the peripherally disposed fibers are not always equally spaced about the central fiber. A maximum of six fibers can be equally spaced about the central fiber and yet be in contact with the central fiber.